topic 10: equilibrium I Flashcards
what is dynamic equilibrium
occurs when forward and backward reactions are occurring at equal rates. the
concentrations of reactants and products stays
constant and the reaction is continuous
what does Le Chatelier’s principle state
if an external
condition is changed the equilibrium will shift to
oppose the change (and try to reverse it)
what happens to the equilibrium when the temperature increases
if temperature is increased the equilibrium will
shift to oppose this and move in the
endothermic direction to try to reduce the
temperature by absorbing heat
what happens to the equilibrium when the temperature decreases
if temperature is decreased the equilibrium will shift to oppose this and move in the exothermic direction to try to increase the
temperature by giving out heat
what happens to the equilibrium when pressure increases
increasing pressure will cause the equilibrium to shift
towards the side with fewer moles of gas to oppose
the change and thereby reduce the pressure
what happens to equilibrium when pressure decreases
Decreasing pressure will cause the equilibrium to shift
towards the side with more moles of gas to oppose
the change and thereby increase the pressure
if the number of moles of gas is the same on both
sides of the equation then changing pressure will have
no effect on the position of equilibrium
H2 + Cl2 —> 2HCl
what is the effect on concentration on equilibrium
I2 + 2OH- <—–> I- + IO- + H2O
increasing the concentration OH ions causes the equilibrium to shift to oppose this and move in the forward direction to remove OH- ions. the
position of equilibrium will shift towards the right, giving a higher yield
of I- and IO-. ( the colour would change from brown to colourless)
adding H+ ions reacts with the OH ions and reduces their concentration
so the equilibrium shifts back to the left giving brown colour
what is the effect of catalyst on equilibrium
a catalyst has no effect on the position of equilibrium, but it will speed up the rate at which the
equilibrium is achieved
it does not effect the position of equilibrium because it speeds up the rates of the forward and backward reactions by the same amount
the haber process
T= 450oC, P= 200 – 1000 atm, catalyst = iron
- low temp gives good yield but slow rate: compromise temp used
- high pressure gives good yield and high rate: too high a pressure would lead to too high energy costs for pumps to produce the pressure
contact process
Stage 1: S(s) + O2(g) —> SO2(g)
Stage 2: SO2 (g) + ½ O2 (g) <—> SO3 (g) H = -98 kJ mol-1
T= 450oC, P= 1 to 2 atm, catalyst = V2O5
- low temp gives good yield but slow rate: compromise
moderate temp used
- high pressure gives slightly better yield and high rate: too
high a pressure would lead to too high energy costs for
pumps to produce the pressure
production of methanol from CO
CO(g) + 2H2(g) <—> CH3OH (g) H = -ve exo
T= 400oC, P= 50 atm, catalyst = chromium and zinc oxides
- low temp gives good yield but slow rate: compromise temp used
- high pressure gives good yield and high rate: too high a pressure would lead to too high energy costs for pumps to produce the pressure
hydration of ethene to produce ethanol
CH2=CH2(g) + H2O(g) <—> CH3CH2OH(l) H = -ve
T= 300oC, P= 70 atm, catalyst = conc H3PO4
- low temp gives good yield but slow rate: compromise
temp used
- high pressure gives good yield and high rate: too high a
pressure would lead to too high energy costs for pumps
to produce the pressure
- high pressure also leads to unwanted polymerisation of
ethene to poly(ethene)
what is the general formula of Kc
=[C]p[D]q/[A]m[B]n
mA + nB <—> pC + qD
the larger the Kc….
the greater the amount of products
what is Kc affected by
Kc only changes with temperature
it does not change if pressure or
concentration is altered. a catalyst also has no effect on Kc
